28" has never been commonly used as a designation in the USA but has been used in Europe to refer to 700C (622 mm ISO) tires. Not sure why as most traditional road tire diameters are closer to 27" than 28". There were also 28" rims used in Holland, UK, India, Sweden and China that were 635 mm. I've never measured one but I'd guess tires for those rims are actually fairly close to 28" diameter.I was to believe 700c is 28 inch . F700 can just about run 28mm Front and 35mm rear . Also I thought 29 was just 28’s with fatter tyres